The comet assay (single-cell gel test). A sensitive genotoxicity test for the detection of DNA damage and repair

Boron Compounds Exhibit Protective Effects against Aluminum-Induced Neurotoxicity and Genotoxicity: In Vitro and In Vivo Study

Genetic, neuropathological and biochemical investigations have revealed meaningful relationships between aluminum (Al) exposure and neurotoxic and hematotoxic damage. Hence, intensive efforts are being made to minimize the harmful effects of Al. Moreover, boron compounds are used in a broad mix of industries, from cosmetics and pharmaceuticals to agriculture. They affect critical biological functions in cellular events and enzymatic reactions, as well as endocrinal and mineral metabolisms. There are limited dose-related data about boric acid (BA) and other boron compounds, including colemanite (Col), ulexite (UX) and borax (BX), which have commercial prominence. In this study, we evaluate boron compounds’ genetic, cytological, biochemical and pathological effects against aluminum chloride (AlCl₃)-induced hematotoxicity and neurotoxicity on different cell and animal model systems. First, we perform genotoxicity studies on in vivo rat bone marrow cells and peripheric human blood cultures. To analyze DNA and chromosome damage, we use single cell gel electrophoresis (SCGE or comet assay) and micronucleus (MN) and chromosome aberration (CA) assays. The nuclear division index (NDI) is used to monitor cytostasis. Second, we examine the biochemical parameters (superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px), malondialdehyde (MDA), total antioxidant capacity (TAC) and total oxidative status (TOS)) to determine oxidative changes in blood and brain. Next, we assess the histopathological alterations by using light and electron microscopes. Our results show that Al increases oxidative stress and genetic damage in blood and brain in vivo and in vitro studies. Al also led to severe histopathological and ultrastructural alterations in the brain. However, the boron compounds alone did not cause adverse changes based on the above-studied parameters. Moreover, these compounds exhibit different levels of beneficial effects by removing the harmful impact of Al. The antioxidant, antigenotoxic and cytoprotective effects of boron compounds against Al-induced damage indicate that boron may have a high potential for use in medical purposes in humans. In conclusion, our analysis suggests that boron compounds (especially BA, BX and UX) can be administered to subjects to prevent neurodegenerative and hematological disorders at determined doses.

Evaluation of Genetic Damage and Antigenotoxic Effect of Ascorbic Acid in Erythrocytes of Orochromis niloticus and Ambystoma mexicanum Using Migration Groups as a Parameter

The comet assay system is an efficient method used to assess DNA damage and repair; however, it currently provides the average result and, unfortunately, the heterogeneity of DNA damage loses relevance. To take advantage of this heterogeneity, migration groups (MGs) of cell comets can be formed. In this study, genetic damage was quantified in erythrocytes of Oreochromis niloticus and Ambystoma mexicanum exposed to ethyl methanesulfonate (ethyl methanesulfonate (EMS) 2.5, 5, and 10 mM over two hours) and ultraviolet C radiation (UV-C) for 5, 10, and 15 min using the tail length, tail moment, and migration group parameters. Additionally, blood cells were exposed to UV-C radiation for 5 min and treated post-treatment at 5, 10, and 15 mM ascorbic acid (AA) for two hours. With the MG parameter, it was possible to observe variations in the magnitude of genetic damage. Our data indicate that MGs help to detect basal and induced genetic damage or damage reduction with approximately the same efficiency of the tail length and tail moment parameters. MGs can be a complementary parameter used to assess DNA integrity in species exposed to mutagens.

Effects of long-term fluoride exposure are associated with oxidative biochemistry impairment and global proteomic modulation, but not genotoxicity, in parotid glands of mice

BACKGROUND

Fluoride has become widely used in dentistry because of its effectiveness in caries control. However, evidence indicates that excessive intake interferes with the metabolic processes of different tissues. Thus, this study aimed to investigate the effects of long-term exposure to F on the parotid salivary gland of mice, from the analysis of oxidative, proteomic and genotoxic parameters.

MATERIALS AND METHODS

The animals received deionized water containing 0, 10 or 50 mg/L of F, as sodium fluoride, for 60 days. After, parotid glands were collected for analysis of oxidative biochemistry, global proteomic profile, genotoxicity assessment and histopathological analyses.

RESULTS

The results revealed that exposure to fluoride interfered in the biochemical homeostasis of the parotid gland, with increased levels of thiobarbituric acid reactive species and reduced glutathione in the exposed groups; as well as promoted alteration of the glandular proteomic profile in these groups, especially in structural proteins and proteins related to oxidative stress. However, genotoxic assessment demonstrated that exposure to fluoride did not interfere with DNA integrity in these concentrations and durations of exposure. Also, it was not observed histopathological alterations in parotid gland.

CONCLUSIONS

Thus, our results suggest that long-term exposure to fluoride promoted modulation of the proteomic and biochemical profile in the parotid glands, without inducing damage to the genetic component. These findings reinforce the importance of rationalizing the use of fluorides to maximize their preventative effects while minimizing the environmental risks.

Effects of Fluoride on Submandibular Glands of Mice: Changes in Oxidative Biochemistry, Proteomic Profile, and Genotoxicity

Although fluoride (F) is well-known to prevent dental caries, changes in cell processes in different tissues have been associated with its excessive exposure. Thus, this study aimed to evaluate the effects of F exposure on biochemical, proteomic, and genotoxic parameters of submandibular glands. Twenty one old rats (n = 30) were allocated into three groups: 60 days administration of drinking water containing 10 mgF/L, 50 mgF/L, or only deionized water (control). The submandibular glands were collected for oxidative biochemistry, protein expression profile, and genotoxic potential analyses. The results showed that both F concentrations increased the levels of thiobarbituric acid–reactive substances (TBARS) and reduced glutathione (GSH) and changed the proteomic profile, mainly regarding the cytoskeleton and cellular activity. Only the exposure to 50 mgF/L induced significant changes in DNA integrity. These findings reinforce the importance of continuous monitoring of F concentration in drinking water and the need for strategies to minimize F intake from other sources to obtain maximum preventive/therapeutic effects and avoid potential adverse effects.

Cupric Oxide Nanoparticles Induce Cellular Toxicity in Liver and Intestine Cell Lines

Purpose: The wide application of cupric oxide nanoparticles (copper (II) oxide, CuO-NPs) in various fields has increased exposure to the kind of active nanomaterials, which can cause negative effects on human and environment health. Although CuO-NPs were reported to be harmful to human, there is still a lack information related to their toxic potentials. In the present study, the toxic potentials of CuO-NPs were evaluated in the liver (HepG2 hepatocarcinoma) and intestine (Caco-2 colorectal adenocarcinoma) cells. Methods: After the characterization of particles, cellular uptake and morphological changes were determined. The potential of cytotoxic, genotoxic, oxidative and apoptotic damage was investigated with several in vitro assays. Results: The average size of the nanoparticles was 34.9 nm, about 2%-5% of the exposure dose was detected in the cells and mainly accumulated in different organelles, causing oxidative stress, cell damages, and death. The IC50 values were 10.90 and 10.04 µg/mL by MTT assay, and 12.19 and 12.06 µg/mL by neutral red uptake (NRU) assay, in HepG2 and Caco-2 cells respectively. Apoptosis assumes to the main cell death pathway; the apoptosis percentages were 52.9% in HepG2 and 45.5% in Caco-2 cells. Comet assay result shows that the highest exposure concentration (20 µg/mL) causes tail intensities about 9.6 and 41.8%, in HepG2 and Caco-2 cells, respectively. Conclusion: CuO-NPs were found to cause significant cytotoxicity, genotoxicity, and oxidative and apoptotic effects in both cell lines. Indeed, CuO-NPs could be dangerous to human health even if their toxic mechanisms should be elucidated with further studies.

Assessment of Genotoxic Effects of Pendimethalin in Chinese Hamster Over Cells by the Single Cell Gel Electrophoresis (Comet) Assay

Objectives

Pendimethalin (N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzeneamine) is a dinitroaniline herbicide compound which selectively controls weeds. It is a cell division and growth inhibitor. It descends plants in a short time after seedling. It is a soil and water pollutant due to the widespread use of formulations in Turkey and around the world. Pendimethalin is manufactured in and imported by Turkey. Pendimethalin is a slightly toxic compound that is classified in toxicity class 3 by the United States Environmental Protection Agency (USEPA). Even though it is classified as group C (human possible carcinogen) compound by the USEPA, there are limited number of studies about its genotoxic effects. The aim of this study was to evaluate in vitro genotoxic effects of different concentrations of pendimethalin in Chinese hamster over (CHO) cells by the single cell gel electrophoresis (comet) assay.

Materials and Methods

The cells are incubated with 1, 10, 100, 1000 and 10000 µM concentrations of pendimethalin for 30 min at 37°C and DNA damage was compared with CHO cells untreated with pendimethalin. 50 µM hydrogen peroxide was used as positive control.

Results

No significant cytotoxic effects were observed within the concentration ranges studied. The DNA damage in CHO cells was significantly increased in the pendimethalin concentrations of 1, 100, 1000 and 10000 µM, however, a significant decrease was observed in 10 µM pendimethalin concentration.

Conclusion

Our results show that 1-10000 µM concentrations of pendimethalin induce DNA damage in CHO cells, which was assessed by comet assay.

In Vitro Evaluation of the Toxicity of Cobalt Ferrite Nanoparticles in Kidney Cell

Objectives

The remarkable properties of hard magnetic cobalt ferrite nanoparticles (CoFe₂O₄-NPs) and their physicochemical stability lead to various applications in different industrial and medical fields. Although CoFe₂O₄-NPs have been reported to cause toxic effects, there is a serious lack of information concerning their effects on the kidneys. In this study, it was aimed to investigate the toxic effects of CoFe₂O₄-NPs on NRK-52E kidney cells.

Materials and Methods

The particle characterisation and cellular uptake were determined using transmission electron microscopy, dynamic light scattering and inductively coupled plasma-mass spectrometry. Then, the cytotoxicity was evaluated by MTT and neutral red uptake assays, the genotoxicity by comet assay, and the apoptotic potentials by Annexin V-FITC apoptosis detection assay with propidium iodide.

Results

After 24 h exposure to CoFe₂O₄-NPs (39±17 nm), it was observed they did not affect the cell viability at concentration ranging from 100 to 1000 µg/mL, but significantly induced DNA damage at concentration ≤100 µg/mL. No apoptotic or necrotic effect was observed in the exposed cells.

Conclusion

According to the results obtained, CoFe₂O₄-NPs are promising for safe use in various applications. However, further in vivo studies are needed to fully understand their mechanisms of action.

Investigation of the toxicity of bismuth oxide nanoparticles in various cell lines

Nanoparticles have been drawn attention in various fields ranging from medicine to industry because of their physicochemical properties and functions, which lead to extensive human exposure to nanoparticles. Bismuth (Bi)-based compounds have been commonly used in the industrial, cosmetic and medical applications. Although the toxicity of Bi-based compounds was studied for years, there is a serious lack of information concerning their toxicity and effects in the nanoscale on human health and environment. Therefore, we aimed to investigate the toxic effects of Bi (III) oxide (Bi₂O₃) nanoparticles in liver (HepG2 hepatocarcinoma cell), kidney (NRK-52E kidney epithelial cell), intestine (Caco-2 colorectal adenocarcinoma cell), and lung (A549 lung carcinoma cell) cell cultures. Bi₂O₃ nanoparticles (∼149.1 nm) were easily taken by all cells and showed cyto- and genotoxic effects. It was observed that the main cell death pathways were apoptosis in HepG2 and NRK-52E cells and necrosis in A549 and Caco-2 cells exposed to Bi₂O₃ nanoparticles. Also, the glutathione (GSH), malondialdehyde (MDA), and 8-hydroxy deoxyguanine (8-OHdG) levels were significantly changed in HepG2, NRK-52E, and Caco-2 cells, except A549 cell. The present study is the first to evaluate the toxicity of Bi₂O₃ nanoparticles in mammalian cells. Bi₂O₃ nanoparticles should be thoroughly assessed for their potential hazardous effects to human health and the results should be supported with in vivo studies to fully understand the mechanism of their toxicity.

In Vitro Toxicological Assessment of Cobalt Ferrite Nanoparticles in Several Mammalian Cell Types

Nanoparticles have been widely used in various fields due to the superior physicochemical properties and functions. As a result, human exposure to nanoparticles increases dramatically. Previous researches have shown that nanoparticles could travel through the respiratory, digestive system, or skin into the blood and then to the secondary organs such as the brain, heart, and liver. Besides, the nanoparticle toxicity is controversial and dependent on the sensitivity of the cell type, route of exposure, and condition, as well as their characteristics. Similarly, cobalt ferrite nanoparticles (CoFe₂O₄-NPs) have been used in different industrial fields, and have also various application possibilities in medical and biomedical fields. CoFe₂O₄-NPs induce toxic responses in various organisms such as human, mice, and algae. However, there is a serious deficit of information concerning their effects on human health and the environment. We aimed to investigate the toxic effects of CoFe₂O₄-NPs on liver (HepG2), colon (Caco-2), lung (A549), and neuron (SH-SY5Y) cells, which reflect different exposure routes in vitro, by using various toxicological endpoints. The cytotoxicity, genotoxicity, oxidative damage, and apoptosis induction of CoFe₂O₄-NPs (39 ± 17 nm) were evaluated. After 24 h, the nanoparticles decreased cell viability at ≤100 μg/mL, while increasing viability at >100 μg/mL. CoFe₂O₄-NPs induced DNA and oxidative damage with increased malondialdehyde (MDA) and 8-hydroxy deoxyguanosine (8-OHdG) levels and decreased glutathione (GSH) levels with no change in protein carbonyl (PC) levels. CoFe₂O₄-NPs had apoptotic effect in HepG2 and Caco-2 cells in a concentration-dependent manner and necrotic effects on SH-SY5Y and A549 cells. Consequently, the adverse effects of CoFe₂O₄-NPs should raise concern about their safety in consumer products.

Nickel oxide nanoparticles are highly toxic to SH-SY5Y neuronal cells

Nickel oxide nanoparticles (NiO-NPs) are used in many industrial sectors including printing inks, ceramics and catalysts, and electrical and electronics industry because of their magnetic and optical properties. However, there has been still a serious lack of information about their toxicity at the cellular and molecular levels on nervous system. For that, we aimed to investigate the in vitro toxic potentials of NiO-NPs in neuronal (SH-SY5Y) cells. The particle characterisation, cellular uptake and morphological changes were determined using Transmission Electron Microscopy, dynamic light scattering and Inductively Coupled Plasma-Mass Spectrometry. Then, the cytotoxicity was evaluated by MTT and neutral red uptake assays, the genotoxicity by comet assay, the oxidative potentials by the determination of malondialdehyde, 8-hydroxy deoxyguanosine, protein carbonyl, and glutathione levels with Enzyme-Linked Immune Sorbent Assays, and the apoptotic potentials by Annexin V-FITC apoptosis detection assay with propidium iodide. According to the results, it was observed that NiO-NPs (15.0 nm ± 4.2-38.1 nm); (i) were taken up by the cells in concentration dependent manner, (ii) caused 50% inhibition in cell viability at ≥229.34 μg/mL, (iii) induced some morphological changes, (iv) induced dose-dependent DNA damage (3.2-11.0 fold) and apoptosis (80-99%), (v) significantly induced oxidative damage. In conclusion, our results support the hypothesis that NiO-NPs affect human health especially neuronal system negatively and should raise the concern about the safety associated with their applications in consumer products.

Gold Nanoparticles in Single-Cell Analysis for Surface Enhanced Raman Scattering

The need for new therapeutic approaches in the treatment of challenging diseases such as cancer, which often consists of a highly heterogeneous and complex population of cells, brought up the idea of analyzing single cells. The development of novel techniques to analyze single cells has been intensively studied to fully understand specific alternations inducing abnormalities in cellular function. One of the techniques used for single cell analysis is surface-enhanced Raman spectroscopy (SERS) in which a noble metal nanoparticle is used to enhance Raman scattering. Due to its low toxicity and biocompatibility, gold nanoparticles (AuNPs) are commonly preferred as SERS substrates in single cell analysis. The intracellular uptake, localization and toxicity issues of AuNPs are the critical points for interpretation of data since the obtained SERS signals originate from molecules in close vicinity to AuNPs that are taken up by the cells. In this review, the AuNP-living cell interactions, cellular uptake and toxicity of AuNPs in relation to their physicochemical properties, and surface-enhanced Raman scattering from single cells are discussed.

Bioavailability of pollutants sets risk of exposure to biota and human population in reservoirs from Iguaçu River (Southern Brazil)

The Iguaçu River, located at the Southern part of Brazil, has a great socioeconomic and environmental importance due to its high endemic fish fauna and its potential to generate hydroelectric power. However, Iguaçu River suffers intense discharge of pollutants in the origin of the river. In a previous report, the local environmental agency described water quality to improve along the river course. However, no study with integrated evaluation of chemical analysis and biological responses has been reported so far for the Iguaçu River. In the current study, three different Brazilian fish species (Astyanax bifasciatus, Chrenicicla iguassuensis, and Geophagus brasiliensis) were captured in the five cascading reservoirs of Iguaçu River for a multi-biomarker study. Chemical analysis in water, sediment, and muscle indicated high levels of bioavailable metals in all reservoirs. Polycyclic aromatic hydrocarbons (PAHs) were detected in the bile of the three fish species. Integration of the data through a FA/PCA analysis demonstrated the poorest environmental quality of the reservoir farthest from river's source, which is the opposite of what has been reported by the environmental agency. The presence of hazardous chemicals in the five reservoirs of Iguaçu River, their bioaccumulation in the muscle of fish, and the biological responses showed the impacts of human activities to this area and did not confirm a gradient of pollution between the five reservoirs, from the source toward Iguaçu River's mouth. Therefore, diffuse source of pollutants present along the river course are increasing the risk of exposure to biota and human populations.

Evaluation of DNA damage and DNA repair capacity in occupationally lead-exposed workers

Occupational lead (Pb) exposure remains a significant concern for workers in Turkey. Health hazards of Pb exposure have been investigated in various test systems, but results regarding its potential genotoxic effects on exposed populations are contradictory. In this study, a control group and an exposed group were studied, each consisting of 25 male subjects. Blood lead levels (BLLs) were estimated by graphite furnace atomic absorption spectrometry. Genotoxic effects of Pb exposure were studied in leukocytes by comet and challenge assays. The effect of Pb exposure to DNA repair capacity was evaluated following in vitro hydrogen peroxide exposure. Pb-exposed workers had significantly higher BLLs than the control group ( p < 0.01). DNA damage in exposed workers had a significantly higher percentage of DNA in tail than the control group ( p < 0.05). In the challenge assay, it was found that the mean DNA% repair capacity was significantly decreased in Pb-exposed workers ( p < 0.01). The results indicated that occupational Pb exposure is associated with DNA damage and causes decrease in DNA% repair capacity, indicating a potential health concern for occupationally Pb-exposed populations.

In Vitro Toxicological Assessment of Magnesium Oxide Nanoparticle Exposure in Several Mammalian Cell Types

Worldwide researchers have rising concerns about magnesium-based materials, especially magnesium oxide (MgO) nanaoparticles, due to increasing usage as promising structural materials in various fields including cancer treatment. However, there is a serious lack of information about their toxicity at the cellular and molecular levels. In this study, the toxic potentials of MgO nanoparticles were investigated on liver (HepG2), kidney (NRK-52E), intestine (Caco-2), and lung (A549) cell lines. For the toxicological assessment, the following assays were used: the particle characterization by transmission electron microscopy, the determination of cellular uptake by inductively coupled plasma-mass spectrometry, MTT and neutral red uptake assays for cytotoxicity, comet assay for genotoxicity, and the determination of malondialdehyde (MDA), 8-hydroxydeoxyguanosine, protein carbonyl, and glutathione levels by enzyme-linked immune sorbent assays for the potential of oxidative damage and annexin V-fluorescein isothiocyanate (FITC) apoptosis detection assay with propidium iodide (PI) for apoptosis. Magnesium oxide nanoparticles were taken up by the cells depending on their concentration and agglomeration/aggregation potentials. Magnesium oxide nanoparticles induced DNA (≤14.27 fold) and oxidative damage. At a concentration of ≥323.39 µg/mL, MgO nanoparticles caused 50% inhibition in cell viability by 2 different cytotoxicity assays. The cell sensitivity to cytotoxic and genotoxic damage induced by MgO nanoparticles was ranked as HepG2 < A549 < Caco-2 < NRK-52E. Although it was observed that MgO nanoparticles induced apoptotic effects on the cells, apoptosis was not the main cell death. DNA damage, cell death, and oxidative damage effects of MgO nanoparticles should raise concern about the safety associated with their applications in consumer products.

Mesotrione herbicide promotes biochemical changes and DNA damage in two fish species

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Our results are novel, never before the toxicity of mesotrione was tested with biomarkers in fish

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We assess the acute effects of mesotrione using 9 different biomarkers.

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DNA damage was assessed in three different cell types in two species exposed to mesotrione.

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We found a positive ROS response in O. niloticus and G. brasiliensis induced by mesotrione.

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Adverse effects were found on concentrations lower than the applied on crop fields.

Mesotrione is one of the new herbicides that have emerged as an alternative after the ban of atrazine in the European Union. To our knowledge, any work using genetic or biochemical biomarkers was performed in any kind of fish evaluating the toxicity of this compound. The impact of acute (96 h) exposure to environmentally relevant mesotrione concentrations (1.8, 7, 30, 115 e 460 μg L⁻¹) were evaluated on the liver of Oreochorimis niloticus and Geophagus brasiliensis by assessing the activity of superoxide dismutase (SOD), glutathione peroxidase (GPx) and glutathione-S- transferase (GST), the levels of reduced glutathione (GSH), carbonyl assays (PCO) and lipid peroxide (LPO) as well as the DNA damage to erithrocytes, liver and gills through the comet assay. We observed an increase in the concentration of GSH and the GPx activity in O. niloticus, and the GST and SOD activity in G. brasiliensis. We found significant increase in DNA damage in all tissues in both species. The results indicated that the acute exposure to mesotrione can induce oxidative stress and DNA damage in both species.

Zinc oxide nanoparticles induced cyto- and genotoxicity in kidney epithelial cells

The wide uses of zinc oxide nanoparticles (nano-ZnO) in industrial, cosmetics, medicine, food production and electronics associate with increase in occupational and public exposure. Although, toxicity of nano-ZnO has been extensively studied on many different cell types and animal systems, there is a significant lack of toxicological data focus on nephrotoxic potential of nano-ZnO. In this study, the cyto- and genotoxic effects of nano-ZnO on rat kidney epithelial cells (NRK-52E) were investigated by using different assays. Nano-ZnO (10-50 nm of sizes) were synthesized by sol-gel method. For the cytotoxic effect of nano-ZnO, mean of inhibition concentration (IC50) values in cell line was evaluated by MTT, Trypan Blue (TB) and Neutral Red Uptake (NRU) assays at 25.0-100.0 μg/mL exposure concentrations. Nano-ZnO showed cytotoxic activity by acting on different targets in renal cells, with IC50 ≥ 73.05 μg/mL. Comet assay was used to evaluate the genotoxicity of nano-ZnO (12.5-50.0 μg/mL). Nano-ZnO caused statistically significant DNA damage. Our results highlight the important risk of cyto- and genotoxic effects of nano-ZnO over the kidney.

Investigation on the toxic potential of Tribulus terrestris in vitro

CONTEXT

Tribulus terrestris L. (Zygophyllaceae) has been commonly used to energize, vitalize, and improve sexual function and physical performance in men.

OBJECTIVE

This study investigates the potential cytotoxic and genotoxic, and endocrine disrupting activities of T. terrestris in vitro.

MATERIALS AND METHODS

The whole T. terrestris plant was extracted with water, methanol, and chloroform. The genotoxic potential of T. terrestris extracts at 3-2400 µg/mL was assessed by Comet assay in a rat kidney cell line (NRK-52E) and by Ames assay in Salmonella typhimurium TA98 and TA100 strains. Endocrine disrupting effects of the extracts at concentrations of 0.22-25 000 µg/mL were assessed by YES/YAS assay in Saccharomyces cerevisiae. Cytotoxic activity of the extracts was determined by the MTT test in NRK-52E cells. The different exposure times were used for four tests (3-48 h).

RESULTS

The methanol extract of T. terrestris IC50 value was 160 µg/mL. The other extracts did not show cytotoxic effects. In the Comet and Ames genotoxicity assays, none of the extracts possessed genotoxic activities at concentrations of 0-2400 µg/mL. Only the water extract of T. terrestris induced frame shift mutations after metabolic activation. The water extract also showed estrogenic activity by YES/YAS assay in S. cerevisiae at concentrations ≥27 µg/mL (≥2.6-fold), while the other T. terrestris extracts had anti-estrogenic properties.

CONCLUSION

Tribulus terrestris had estrogenic and genotoxic activities. The study was useful in determining its toxicological effects and the precautions regarding consumption.

Long-term methadone intake and genotoxicity in addicted patients

Background:

It is well known that contact with some physical, chemical or biological compounds can increase the incidence of mutation. Among these compounds, are pharmaceuticals that meet long duration of use and potentially could be misused and taken more than the ordered dosage.

Objectives:

The aim of this study was to evaluate mutagenic effect of methadone in addicted patients referred to Imam Khomeini Hospital in Ahvaz by single cell gel electrophoresis technic or comet assay.

Patients and Methods:

In this study, 90 subjects were divided into dichromate treated group, no treated healthy volunteers group and test group. Each group included 30 subjects. Screening was performed according to questionnaire and qualified subjects were entered the study. Blood samples were collected and lymphocytes were isolated, mixed with low melting point agarose for slide preparation according to standard method. Slides were analyzed using fluorescence microscope and comet patterns were assessed.

Results:

The mutagenicity index in addicted group was robustly higher than healthy volunteers. Fortunately, this significant difference was lower than positive control.

Conclusions:

Genome instability in addicted patients was demonstrated in this study. Controversially, considering incoherent results of previous studies and our data, more studies in longer duration of methadone use are needed to elucidate the consequence.

Assessment of the genotoxic/clastogenic potential of coumarin derivative 6,7-dihydroxycoumarin (aesculetin) in multiple mouse organs

6,7-Dihydroxycoumarin (6,7-HC) (aesculetin) is a natural and synthetic coumarin derivative of great interest for use by humans due to their potent antioxidant properties. Considering that there are no reports that assess the in vivo genetic toxicity of 6,7-HC, the aim of the present study was to investigate its genotoxic potential in terms of DNA damage in peripheral blood, liver, bone marrow and testicular cells of Swiss albino mice by the comet assay, and its clastogenic/aneugenic potential in bone marrow cells using the micronucleus test. In addition, the ability of 6,7-HC to modulate the genotoxic effects induced by doxorubicin (DXR) was also preliminarily evaluated. Cytotoxicity was assessed by scoring polychromatic (PCE) and normochromatic (NCE) erythrocytes’ ratio. The test compound was administered orally at doses of 25, 50 and 500 mg kg⁻¹ isolated and also simultaneously to DXR (80 mg kg⁻¹). The results showed that 6,7-HC did not induce significant DNA damage in any of the analyzed cells, and also did not show any significant increase in micronucleated PCE at the three tested doses. The PCE/NCE ratio indicated no cytotoxicity. Moreover, the extent of DNA damage induced by DXR decreased significantly only in peripheral blood and testicular cells, and only at the lowest dose of 6,7-HC.

PKCη promotes senescence induced by oxidative stress and chemotherapy

Senescence is characterized by permanent cell-cycle arrest despite continued viability and metabolic activity, in conjunction with the secretion of a complex mixture of extracellular proteins and soluble factors known as the senescence-associated secretory phenotype (SASP). Cellular senescence has been shown to prevent the proliferation of potentially tumorigenic cells, and is thus generally considered a tumor suppressive process. However, some SASP components may act as pro-tumorigenic mediators on premalignant cells in the microenvironment. A limited number of studies indicated that protein kinase C (PKC) has a role in senescence, with different isoforms having opposing effects. It is therefore important to elucidate the functional role of specific PKCs in senescence. Here we show that PKCη, an epithelial specific and anti-apoptotic kinase, promotes senescence induced by oxidative stress and DNA damage. We further demonstrate that PKCη promotes senescence through its ability to upregulate the expression of the cell cycle inhibitors p21^Cip1 and p27^Kip1 and enhance transcription and secretion of interleukin-6 (IL-6). Moreover, we demonstrate that PKCη creates a positive loop for reinforcing senescence by increasing the transcription of both IL-6 and IL-6 receptor, whereas the expression of IL-8 is specifically suppressed by PKCη. Thus, the presence/absence of PKCη modulates major components of SASP. Furthermore, we show that the human polymorphic variant of PKCη, 374I, that exhibits higher kinase activity in comparison to WT-374V, is also more effective in IL-6 secretion, p21^Cip1 expression and the promotion of senescence, further supporting a role for PKCη in senescence. As there is now considerable interest in senescence activation/elimination to control tumor progression, it is first crucial to reveal the molecular regulators of senescence. This will improve our ability to develop new strategies to harness senescence as a potential cancer therapy in the future.

Drosophila comet assay: insights, uses, and future perspectives

The comet assay, a very useful tool in genotoxicity and DNA repair testing, is being applied to Drosophila melanogaster since around 15 years ago, by several research groups. This organism is a valuable model for all kind of processes related to human health, including DNA damage response. The assay has been performed mainly in vivo using different larvae cell types (from brain, midgut, hemolymph, and imaginal disk), but also in vitro with the S2 cell line. Since its first application, it has been used to analyze the genotoxicity and action mechanisms of different chemicals, demonstrating good sensitivity and proving its usefulness. Moreover, it is the only assay that can be used to analyze DNA repair in somatic cells in vivo, comparing the effects of chemicals in different repair strains, and to quantitate repair activities in vitro. Additionally, the comet assay in Drosophila, in vivo and in vitro, has been applied to study the influence of protein overexpression on genome integrity and degradation. Although the assay is well established, it could benefit from some research to determine optimal experimental design to standardize it, and then to allow comparisons among laboratories independently of the chosen cell type.

Mechanistic insight into beta-carotene-mediated protection against ulcerative colitis-associated local and systemic damage in mice

PURPOSE

Ulcerative colitis (UC), a chronic gastrointestinal disorder, is a debilitating disease affecting many people across the globe. Research suggests that the levels of several antioxidants, including β-carotene (β-CAR), decrease in the serum of patients with UC. The present study was aimed at elucidating the molecular mechanisms involved in β-CAR-mediated protection against UC in mice.

METHODS

UC was induced in mice using 3%w/v dextran sulfate sodium in drinking water for two cycles; one cycle comprised of 7 days of dextran sulfate sodium-treated water followed by 14 days of normal drinking water. β-CAR was administered at the doses of 5, 10 and 20 mg/kg bw/day, po throughout the experiment. The effect of β-CAR in mice with UC was evaluated using biochemical parameters, histological evaluation, comet and micronucleus assays, immunohistochemistry and Western blot analysis.

RESULTS

The results indicated that β-CAR treatment ameliorated the severity of UC by modulating various molecular targets such as nuclear factor-kappa B, cyclooxygenase-2, interleukin 17, signal transducer and activator of transcription 3, nuclear erythroid 2-related factor 2, matrix metalloproteinase-9 and connective tissue growth factor. Further, β-CAR treatment maintained the gut integrity by increasing the expression of a tight junction protein, occludin, which was decreased in the colon of mice with UC. Also β-CAR treatment significantly reduced UC-associated elevated plasma lipopolysaccharide level, systemic inflammation and genotoxicity.

CONCLUSION

β-CAR ameliorated UC-associated local and systemic damage in mice by acting on multiple targets.

New therapy of skin repair combining adipose-derived mesenchymal stem cells with sodium carboxymethylcellulose scaffold in a pre-clinical rat model

Lesions with great loss of skin and extensive burns are usually treated with heterologous skin grafts, which may lead rejection. Cell therapy with mesenchymal stem cells is arising as a new proposal to accelerate the healing process. We tested a new therapy consisting of sodium carboxymethylcellulose (CMC) as a biomaterial, in combination with adipose-derived stem cells (ADSCs), to treat skin lesions in an in vivo rat model. This biomaterial did not affect membrane viability and induced a small and transient genotoxicity, only at the highest concentration tested (40 mg/mL). In a rat wound model, CMC at 10 mg/mL associated with ADSCs increased the rate of cell proliferation of the granulation tissue and epithelium thickness when compared to untreated lesions (Sham), but did not increase collagen fibers nor alter the overall speed of wound closure. Taken together, the results show that the CMC is capable to allow the growth of ADSCs and is safe for this biological application up to the concentration of 20 mg/mL. These findings suggest that CMC is a promising biomaterial to be used in cell therapy.

Benzophenone guttiferone A from Garcinia achachairu Rusby (Clusiaceae) presents genotoxic effects in different cells of mice

Benzophenones from natural sources and those of synthetic analogues present several reports of potent biological properties, and Guttiferone A represents a promising medicinal natural compound with analgesic and gastroprotective profiles. Considering that there are no reports that assess the genetic toxicity of Guttiferone A, the present study was undertaken to investigate the genotoxic potential of this benzophenone isolated from seeds of Garcinia achachairu in terms of DNA damage in different cells of Swiss albino mice using the comet assay, and its clastogenic/aneugenic effects in bone marrow cells in vivo by the micronucleus test. Cytotoxicity was assessed by scoring polychromatic (PCE) and normochromatic (NCE) erythrocytes ratio. Guttiferone A was administered by oral gavage at doses of 15, 30 and 60 mg/kg. The results showed that Guttiferone A produced genotoxic effects in leukocytes, liver, bone marrow, brain and testicle cells and clastogenic/aneugenic effects in bone marrow erythrocytes of mice. The PCE/NCE ratio indicated no cytotoxicity. Since guttiferone A is harmful to the genetic material we suggest caution in its use by humans.

Differences in Phosphorylated Histone H2AX Foci Formation and Removal of Cells Exposed to Low and High Linear Energy Transfer Radiation

The use of particle ion beams in cancer radiotherapy has a long history. Today, beams of protons or heavy ions, predominantly carbon ions, can be accelerated to precisely calculated energies which can be accurately targeted to tumors. This particle therapy works by damaging the DNA of tissue cells, ultimately causing their death. Among the different types of DNA lesions, the formation of DNA double strand breaks is considered to be the most relevant of deleterious damages of ionizing radiation in cells. It is well-known that the extremely large localized energy deposition can lead to complex types of DNA double strand breaks. These effects can lead to cell death, mutations, genomic instability, or carcinogenesis. Complex double strand breaks can increase the probability of mis-rejoining by NHEJ. As a consequence differences in the repair kinetics following high and low LET irradiation qualities are attributed mainly to quantitative differences in their contributions of the fast and slow repair component. In general, there is a higher contribution of the slow component of DNA double strand repair after exposure to high LET radiation, which is thought to reflect the increased amount of complex DNA double strand breaks. These can be accurately measured by the γ-H2AX assay, because the number of phosphorylated H2AX foci correlates well with the number of double strand breaks induced by low or / and high LET radiation.

Effect of low-osmolar contrast medium iopromide and iso-osmolar iodixanol on DNA fragmentation in renal tubular cell culture

BACKGROUND

Intravascular administration of iodinated contrast media continues to be a common cause of hospital-acquired acute kidney injury. Accumulating evidence suggests that radiocontrast agent-induced nephrotoxicity is associated with increased oxidative stress, which leads to renal tissue damage with DNA fragmentation. We therefore tested whether an iso-osmolar contrast medium (iodixanol) causes less oxidative DNA damage to renal tubular cells than a low-osmolar contrast medium (iopromide).

METHODS

HK-2 cells (human proximal renal tubular cell line) were incubated at different time points (10 min-2 h) with increasing concentrations (20-120 mg/ml iodine) of iodixanol or of iopromide. Oxidative DNA damage to renal tubular cells was measured by alkaline comet assay (single-cell gel electrophoresis).

RESULTS

Both iso- and low-osmolar contrast agents induced time- and concentration-dependent DNA fragmentation. DNA fragmentation was maximal at 2 h with 120 mg/ml iodine for iopromide (32 ± 27 tail moments) and iodixanol (46 ± 41 tail moments); both were significantly different from the control value with 3.15 ± 1.6 tail moments (Student's t test; p < 0.001). After 1 and 2 h and for all concentrations, iodixanol produced significantly higher DNA fragmentation than iopromide (ANOVA for 1 h p = 0.039 and 2 h p = 0.025, respectively).

CONCLUSION

We were able to demonstrate for the first time that an iso-osmolar contrast medium induced even greater oxidative stress and DNA damage than a low-osmolar agent in HK-2 cells. This could provide an explanation for the nephrotoxicity that also is observed with iodixanol in clinical practice.

Determination of the mutagenicity potential of dillsun herbal medicine by single cell gel electrophoresis in rat hepatocytes

BACKGROUND

Traditional medicines are among the oldest medicines and their extensive use in the recent years reflects the public's interest in alternatives to conventional medicine.

OBJECTIVES

The aim of this study was to investigate the genotoxicity of Dillsun herbal medicine in DNA damage of rat hepatocytes compared to sodium dichromate using a comet assay technique.

MATERIALS AND METHODS

Male Wistar rats were caught and their liver was washed with a perfusion buffer, followed by another wash with collagenase buffer. Hepatocytes were isolated and transferred on to a petri dish which contained a washing buffer. Hepatocytes were then separated and the cells were filtered and centrifuged at 1500 rpm for 3 minutes. The hepatocytes were counted using neubauer slides and kept in a bioreactor for 30 minutes. Cells were then exposed to different doses of Dillsun such 0.2, 1, 2.5, 5 and 10 mg/mL. Sodium dichromate was the positive control and incubated buffer was used as a negative control. Cell suspensions were placed on slides pre-coated with low melting point agarose and were covered with agarose gel. Agarose gels were then lysed and electrophoresis was done, followed by neutralization and staining. Slides were analyzed by fluorescence microscopy. The size and extent of DNA damage visualized by this technique was evaluated by examining cells. Migration behavior was classified according to the Kobayashi pattern.

RESULTS

The results indicated that with an increase of Dillsun dose, the mutagenicity index slightly increased but compared to the positive control, there were significant differences, which suggests that the crude extract of Dillsun in vitro did not have mutagenic effects.

CONCLUSIONS

In conclusion the results showed that Dillsun has no mutagenic effects when compared to the positive control. Although by increasing the Dillsun dose, DNA damage also increased but this increase was not significant.

Evaluation of deoxyribonucleic acid toxicity induced by the radiopharmaceutical 99mTechnetium-Methylenediphosphonic acid and by stannous chloride in Wistar rats

Radiopharmaceuticals are employed in patient diagnostics and disease treatments. Concerning the diagnosis aspect, technetium-99m (^99mTc) is utilized to label radiopharmaceuticals for single photon computed emission tomography (SPECT) due to its physical and chemical characteristics. ^99mTc fixation on pharmaceuticals depends on a reducing agent, stannous chloride (SnCl₂) being the most widely-utilized. The genotoxic, clastogenic and anegenic properties of the ^99mTc-MDP(methylene diphosphonate used for bone SPECT) and SnCl₂ were evaluated in Wistar rat blood cells using the Comet assay and micronucleus test. The experimental approach was to endovenously administer NaCl 0.9% (negative control), cyclophosphamide 50 mg/kg b.w. (positive control), SnCl₂ 500 μg/mL or ^99mTc-MDP to animals and blood samples taken immediately before the injection, 3, and 24 h after (in the Comet assay) and 36 h after, for micronucleus test. The data showed that both SnCl₂ and ^99mTc-MDP-induced deoxyribonucleic acid (DNA) strand breaks in rat total blood cells, suggesting genotoxic potential. The ^99mTc-MDP was not able to induce a significant DNA strand breaks increase in in vivo assays. Taken together, the data presented here points to the formation of a complex between SnCl₂ in the radiopharmaceutical ^99mTc-MDP, responsible for the decrease in cell damage, compared to both isolated chemical agents. These findings are important for the practice of nuclear medicine.

Mutagenicity and antimutagenicity of (-)-hinokinin a trypanosomicidal compound measured by Salmonella microsome and comet assays

Background

The dibenzylbutyrolactone lignan (−)-hinokinin (HK) was derived by partial synthesis from (−)-cubebin, isolated from the dry seeds of the pepper, Piper cubeba. Considering the good trypanosomicidal activity of HK and recalling that natural products are promising starting points for the discovery of novel potentially therapeutic agents, the aim of the present study was to investigate the (anti) mutagenic∕ genotoxic activities of HK.

Methods

The mutagenic∕ genotoxic activities were evaluated by the Ames test on Salmonella typhimurium strains TA98, TA97a, TA100 and TA102, and the comet assay, so as to assess the safe use of HK in the treatment of Chagas’ disease. The antimutagenic ∕antigenotoxic potential of HK were also tested against the mutagenicity of a variety of direct and indirect acting mutagens, such as 4- nitro-o-phenylenediamine (NOPD), sodium azide (SA), mitomycin C (MMC), benzo[a]pyrene (B[a]P), aflatoxin B₁ (AFB₁), 2-aminoanthracene (2-AA) and 2-aminofluorene (2-AF), by the Ames test, and doxorubicin (DXR) by the comet assay.

Results

The mutagenicity∕genotoxicity tests showed that HK did not induce any increase in the number of revertants or extent of DNA damage, demonstrating the absence of mutagenic and genotoxic activities. On the other hand, the results on the antimutagenic potential of HK showed a strong inhibitory effect against some direct and indirect-acting mutagens.

Conclusions

Regarding the use of HK as an antichagasic drug, the absence of mutagenic effects in animal cell and bacterial systems is encouraging. In addition, HK may be a new potential antigenotoxic ∕ antimutagenic agent from natural sources. However, the protective activity of HK is not general and varies with the type of DNA damage-inducing agent used.

Determination of the mutagenicity potential of supermint herbal medicine by single cell gel electrophoresis in rat hepatocytes

PURPOSE

The increasing use of herbal drugs and their easy availability have necessitated the use of mutagenicity test to analyze their toxicity and safety. The aim of this study was to evaluate the genotoxicity of Supermint herbal medicine in DNA breakage of rat hepatocytes in comparison with sodium dichromate by single cell gel electrophoresis technique or comet assay.

METHODS

Hepatocytes were prepared from male wistar rats and were counted and kept in a bioreactor for 30 minutes. Then cells were exposed to the Supermint herbal medicine at doses of 125, 250 and 500 µl/ml. Buffer 4 (incubation buffer) and sodium dichromate were used as negative and positive control for one hour respectively. Then cell suspension with low melting point agarose were put on precoated slides and covered with agarose gel. Then lysing, electrophoresis, neutralization and staining were carried out. Finally the slides were analyzed with fluorescence microscope. The parameter under this analysis was the type of migration which was determined according to Kobayashi pattern.

RESULTS

With increased dose of Supermint herbal medicine the DNA damage was slightly increased (P<0001). Conlusion: In overall compared to the positive control significant differences is observed which convinced that the crude extract of Supermint in vitro did not have mutagenic effect. Conlusion: In overall compared to the positive control significant differences is observed which convinced that the crude extract of Supermint in vitro did not have mutagenic effect.

Hepatic oxidative stress in an animal model of sleep apnoea: effects of different duration of exposure

BACKGROUND

Repeated apnoea events cause intermittent hypoxia (IH), which alters the function of various systems and produces free radicals and oxidative stress.

METHODS

We investigated hepatic oxidative stress in adult mice subjected to intermittent hypoxia, simulating sleep apnoea. Three groups were submitted to 21 days of IH (IH-21), 35 days of IH (IH-35), or 35 days of sham IH. We assessed the oxidative damage to lipids by TBARS and to DNA by comet assay; hepatic tissue inflammation was assessed in HE-stained slides. Antioxidants were gauged by catalase, superoxide dismutase, glutathione peroxidase activity and by total glutathione.

RESULTS

After IH-21, no significant change was observed in hepatic oxidative stress. After IH-35, significant oxidative stress, lipid peroxidation, DNA damage and reduction of endogenous antioxidants were detected.

CONCLUSIONS

In an animal model of sleep apnoea, intermittent hypoxia causes liver damage due to oxidative stress after 35 days, but not after 21 days.

Genotoxic effects of (-)-cubebin in somatic cells of mice

(-)-Cubebin belongs to the dibenzylbutyrolactone lignan group, which is widely distributed in the plant kingdom. Because this compound shows interesting biological activities, it is extremely important to evaluate its possible genotoxic activity to allow its safe use in humans. Thus, the present study was performed to investigate the genotoxicity potential activity of (-)-cubebin assessed by two assays: micronucleus in bone marrow cells and comet test in peripheral blood leukocytes of Swiss mice. In the (-)-cubebin dose range-finding assays, the maximum tolerated dose was greater than 2000 mg kg(-1) . The compound was administered by an oral route at single doses of 250, 500 and 2000 mg kg(-1) body weight. Cytotoxicity was assessed by scoring 200 consecutive total polychromatic (PCE) and normochromatic (NCE) erythrocytes (PCE/NCE ratio). Under our experimental conditions, micronucleus and comet assays, respectively, showed that (-)-cubebin caused dose-related clastogenic and genotoxic effects in the somatic cells investigated. PCE/NCE ratio showed no cytotoxicity for the three doses of the compound. The data suggest caution in the ingestion of (-)-cubebin by humans, especially at high doses.

Role of Purα in the cellular response to ultraviolet-C radiation

Purα is a nucleic acid-binding protein with DNA-unwinding activity, which has recently been shown to have a role in the cellular response to DNA damage. We have investigated the function of Purα in Ultraviolet-C (UVC) radiation-induced DNA damage and nucleotide excision repair (NER). Mouse embryo fibroblasts from PURA(-/-) knockout mice, which lack Purα, showed enhanced sensitivity to UVC irradiation as assessed by assays for cell viability and clonogenicity compared to Purα positive control cultures. In reporter plasmid reactivation assays to measure the removal of DNA adducts induced in vitro by UVC, the Purα-negative cells were less efficient in DNA damage repair. Purα-negative cells were also more sensitive to UVC-induced DNA damage measured by Comet assay and showed a decreased ability to remove UVC-induced cyclobutane pyrimidine dimers. In wild-type mouse fibroblasts, expression of Purα is induced following S-phase checkpoint activation by UVC in a similar manner to the NER factor TFIIH. Moreover, co-immunoprecipitation experiments showed that Purα physically associates with TFIIH. Thus, Purα has a role in NER and the repair of UVC-induced DNA damage.

Novel HSP90 inhibitors, NVP-AUY922 and NVP-BEP800, radiosensitise tumour cells through cell-cycle impairment, increased DNA damage and repair protraction

Background:

Heat-shock protein 90 (Hsp90) has a crucial role in both the stabilisation and regulation of various proteins, including those related to radioresistance. Inhibition of Hsp90 may therefore provide a strategy for enhancing the radiosensitivity of tumour cells. This study explores the responses of four tumour cell lines (A549, GaMG, HT 1080 and SNB19) to combined treatment with ionising radiation (IR) and two novel inhibitors of Hsp90, NVP-AUY922 and NVP-BEP800. The techniques used included cell and colony counts, expression of Hsp90, Hsp70, Akt, survivin, cleaved caspase 3, p53, cell-cycle progression and associated proteins. DNA damage was analysed by histone γH2AX and Comet assays.

Results:

We found that NVP-AUY922 and NVP-BEP800 enhanced radiosensitivity in all tested cell lines. In contrast, only two cell lines (HT 1080 and GaMG) exhibited an increased rate of apoptosis after drug pretreatment, as revealed by western blot. In all tested cell lines, the expression of histone γH2AX, a marker of DNA double-strand breaks, after combined drug-IR treatment was higher and its decay rate was slower than those after each single treatment modality. Drug-IR treatment also resulted in impaired cell-cycle progression, as indicated by S-phase depletion and G2/M arrest. In addition, the cell cycle-associated proteins, Cdk1 and Cdk4, were downregulated after Hsp90 inhibition.

Interpretation:

These findings show that the novel inhibitors of Hsp90 can radiosensitise tumour cell lines of different entities through destabilisation and depletion of several Hsp90 client proteins, thus causing the depletion of S phase and G2/M arrest, increased DNA damage and repair protraction and, to some extent, apoptosis. The results might have important implications for the radiotherapy of solid tumours.

Genotoxic evaluation of an industrial effluent from an oil refinery using plant and animal bioassays

Polycyclic aromatic hydrocarbons (PAHs) are genotoxic chemicals commonly found in effluents from oil refineries. Bioassays using plants and cells cultures can be employed for assessing environmental safety and potential genotoxicity. In this study, the genotoxic potential of an oil refinery effluent was analyzed by means of micronucleus (MN) testing of Alium cepa, which revealed no effect after 24 h of treatment. On the other hand, primary lesions in the DNA of rat (Rattus norvegicus) hepatoma cells (HTC) were observed through comet assaying after only 2 h of exposure. On considering the capacity to detect DNA damage of a different nature and of these cells to metabolize xenobiotics, we suggest the association of the two bioassays with these cell types, plant (Allium cepa) and mammal (HTC) cells, for more accurately assessing genotoxicity in environmental samples.

Cytometric assessment of DNA damage induced by DNA topoisomerase inhibitors

Exposure of cells to inhibitors of DNA topoisomerase I (topo I) or topoisomerase II (topo II) leads to DNA damage that often involves formation of DNA double-strand breaks (DSBs). DNA damage, particularly induction of DSBs, manifests by phosphorylation of histone H2AX on Ser-139 which is mediated by one of the protein kinases of the phosphoinositide kinase family, namely ATM, ATR, and/or DNA-PK. The presence of Ser-139 phosphorylated H2AX (gammaH2AX) is thus a reporter of DNA damage. This protocol describes quantitative assessment of gammaH2AX detected immunocytochemically in individual cells combined with quantification of cellular DNA content by cytometry. The bivariate analysis of gammaH2AX expression versus DNA content allows one to correlate DNA damage with the cell cycle phase or DNA ploidy. The protocol can also be used to assess activation (Ser-1981 phosphorylation) of ATM; this event also revealing DNA damage induced by topo I or topo II inhibitors. Examples where DNA damage was induced by topotecan (topo I) and etoposide (topo II) inhibitors are provided.

Protective role of Puralpha to cisplatin

BACKGROUND

The nucleic acid-binding protein Puralpha is involved at stalled DNA replication forks, in double-strand break (DSB) DNA repair and the cellular response to DNA replication stress. Puralpha also regulates homologous recombination-directed DNA repair (HRR).

RESULTS

Cells lacking Puralpha showed enhanced sensitivity to cisplatin as evaluated by assays for cell viability and cell clonogenicity. This was seen both in Puralpha-negative MEFs and in human glioblastoma cells treated with siRNA directed against Puralpha. MEFs lacking Puralpha also showed enhanced H2AX phosphorylation in response to cisplatin. Repair of a reporter plasmid that had been treated with cisplatin was decreased in a reactivation assay using Puralpha-negative MEFs and the capacity of nuclear extracts from Puralpha-negative MEFs to perform non-homologous end-joining in vitro was also impaired.

METHODS

We investigated the effects of the DNA damage-inducing cancer chemotherapeutic agent cisplatin on mouse embryo fibroblasts (MEFs) from PURA(-/-) knockout mice that lack Puralpha.

CONCLUSIONS

Puralpha has a role in the cellular response to cisplatin-induced DNA damage and may provide new therapeutic modalities for cisplatin-resistant tumors.

DNA damage and repair of leukocytes from Fanconi anaemia patients, carriers and healthy individuals as measured by the alkaline comet assay

Fanconi anaemia (FA) patients show cellular sensitivity to a variety of clastogens and prominently to cross-linking agents. Although there is a long-standing clinical impression of radiosensitivity, in vitro studies have yielded conflicting results. In this study, initial radiation-induced DNA damage and kinetics of DNA repair in (60)Co gamma-irradiated leukocytes from healthy volunteers, FA patients and heterozygotes were assessed using alkaline comet assay. Results showed higher levels of baseline DNA damage in leukocytes of patients and heterozygotes than in controls. Gamma-ray-induced initial DNA damage in leukocytes of FA cases was not significantly different from that of healthy donors and heterozygotes. However, after a repair time of 4 h, following irradiation, samples from the healthy individuals and carriers showed less residual DNA damage in their leukocytes, whereas FA patients revealed more DNA damages than their baseline. Although similar initial induced DNA damage was observed for all groups, the repair kinetics of radiation-induced DNA damage of leukocytes from FA patients was statistically different from healthy and carrier subjects. These findings may suggest that hypersensitivity of FA cells to cross-linking and clastogenic agents might be due to inefficient and delayed repair machinery of these cells. Also, the amount of residual DNA damage after irradiation could be used as a putative predictor of FA screening and cellular radiosensitivity.

E2F1 regulates the base excision repair gene XRCC1 and promotes DNA repair

The E2F1 transcription factor activates S-phase-promoting genes, mediates apoptosis, and stimulates DNA repair through incompletely understood mechanisms. XRCC1 (x-ray repair cross-complementing group 1) protein is important for efficient single strand break/base excision repair. Although both damage and proliferative signals increase XRCC1 levels, the mechanisms regulating XRCC1 transcription remain unclear. To study these upstream mechanisms, the XRCC1 promoter was cloned into a luciferase reporter. Ectopic expression of wild-type E2F1, but not an inactive mutant E2F1(132E), activated the XRCC1 promoter-luciferase reporter, and deletion of predicted E2F1 binding sites in the promoter attenuated E2F1-induced activation. Endogenous XRCC1 expression increased in cells conditionally expressing wild-type, but not mutant E2F1, and methyl methanesulfonate-induced DNA damage stimulated XRCC1 expression in E2F1(+/+) but not E2F1(-/-) mouse embryo fibroblasts (MEFs). Additionally, E2F1(-/-) MEFs displayed attenuated DNA repair after methyl methanesulfonate-induced damage compared with E2F1(+/+) MEFs. Moreover, Chinese hamster ovary cells with mutant XRCC1 (EM9) were more sensitive to E2F1-induced apoptosis compared with Chinese hamster ovary cells with wild-type XRCC1 (AA8). These results provide new mechanistic insight into the role of the E2F pathway in maintaining genomic stability.

JC virus agnoprotein inhibits in vitro differentiation of oligodendrocytes and promotes apoptosis

Productive infection of oligodendrocytes, which are responsible for the formation of myelin sheath in the central nervous system, with the human neurotropic virus JC virus (JCV) causes the fatal demyelinating disease progressive multifocal leukoencephalopathy (PML). In addition to encoding T antigen and the capsid proteins, which are produced at the early and late phases of the infection cycle, respectively, JCV encodes a small regulatory protein named agnoprotein that is important for successful completion of the virus life cycle. Here we used bipotential CG-4 cells to examine the impact of agnoprotein on oligodendrocyte differentiation and survival in the absence of JCV lytic infection. We demonstrate that the expression of agnoprotein delayed the formation of complex outgrowth networks of the cells during oligodendrocyte differentiation. These alterations were accompanied by high levels of DNA damage, induction of proapoptotic proteins, and suppression of prosurvival signaling. Accordingly, apoptosis was significantly increased upon the induction of CG-4 cells toward differentiation in cells expressing agnoprotein. These observations provide the first evidence for the possible involvement of agnoprotein, independent from its role in viral replication, in a series of biological events that may contribute to the pathological features seen in PML lesions.

Comparative evaluation of the toxicity and genotoxicity of cadmium in amphibian larvae (Xenopus laevis and Pleurodeles waltl) using the comet assay and the micronucleus test

The toxic and genotoxic potential of Cadmium (CdCl(2)) were evaluated by the micronucleus test (MNT) and comet assay (CA) using amphibian larvae (Xenopus laevis and Pleurodeles waltl). Acute toxicity results showed that Cd is toxic to Xenopus larvae exposed from 2 to 50 mg/L and to Pleurodeles from 5 to 50 mg/L, depending on the nature of the water (reconstituted water containing mineral salts or mineral water MW (Volvic)). The MNT results obtained in MW showed that Cd (2 mg/L) is genotoxic to Xenopus, whereas it was not genotoxic to Pleurodeles at all concentrations tested. The CA established that the genotoxicity of Cd to Xenopus and Pleurodeles larvae depends on the concentration, the exposure times, and the comet parameters (Tail DNA, ETM, OTM, and TL). The CA and MNT results were compared for their ability to detect genotoxic effects, considering the concentrations of Cd applied and the exposure time. The CA showed Cd to be genotoxic from the first day of exposure. In amphibians, the CA appears to be a sensitive and suitable method for detecting genotoxicity such as that caused by Cd.

Radiation-induced DNA damage and repair in peripheral blood mononuclear cells from Nijmegen breakage syndrome patients and carriers assessed by the Comet assay

Nijmegen breakage syndrome (NBS) patients and carriers are predisposed to malignancy and are often treated with X-irradiation. In the present study, the single-cell gel electrophoresis (Comet) assay was used to examine radiation-induced DNA damage and repair in peripheral blood mononuclear cells from NBS patients (n=13) and carriers (n=36) of six unrelated families. Cells from apparently healthy donors (n=10) and from breast cancer patients with normal clinical radiosensitivity (n=10) served as controls. Cells were irradiated with 5 Gy of X-rays and assayed for initial DNA damage and for residual DNA damage after 40 min of repair; the kinetics of DNA repair also was estimated. In addition, the nuclear area of unirradiated cells was extracted from the Comet data. The initial radiation-induced DNA fragmentation indicated that cells from members of two out of six NBS families were significantly more sensitive to X-irradiation than cells from the controls. Cells from four NBS families had longer DNA repair half-time values, while cells from five NBS families had significantly increased residual DNA damage following repair. The mean nuclear area of unirradiated cells processed in the Comet assay was 1.3-fold higher in cells from all NBS families than in the controls (P<0.05). Notably, the Comet assay parameters (initial and residual DNA damage and the repair kinetics) of irradiated NBS cells predicted the carrier status of the majority (86%) of blindly tested individuals. The prediction of NBS status was higher if the nuclear area of unirradiated cells was used as the endpoint. The results of this study suggest that the impaired radiation response of NBS cells should be taken into account if radiotherapy of NBS patients and carriers is required.

Radiosensitivity of lymphoblastoid cell lines with a heterozygous BRCA1 mutation is not detected by the comet assay and pulsed field gel electrophoresis

Lymphoblastoid cell lines (LCL) with a heterozygous mutation in the breast cancer susceptibility gene BRCA1 have been repeatedly used to elucidate the biological consequences of such a mutation with respect to radiation sensitivity and DNA repair deficiency. Our previous results indicated that LCL with a BRCA1 mutation do not generally show the same chromosomal mutagen sensitivity in the micronucleus test as lymphocytes with the same BRCA1 mutation. To further study the radiosensitivity of LCL with a BRCA1 mutation, we now performed comparative investigations with the alkaline (pH 13) and the neutral (pH 8.3) comet assay and pulsed field gel electrophoresis (PFGE). These tests are commonly used to determine the repair capacity for DNA double strand breaks (DNA-DSB). Six LCL (three established from women with a heterozygous BRCA1 mutation and three from healthy controls) were investigated. Induction (2 and 5 Gy) of gamma-ray-induced DNA damage and its repair (during 60 min after irradiation) was measured with the alkaline and neutral comet assay. Comparative experiments were performed with PFGE determining the induction of DNA-DSB by 10-50 Gy gamma-irradiation and their repair during 6 h. There was no significant difference between LCL with and without BRCA1 mutation in any of these experiments. Therefore, using these methods, no indication for a delayed repair of DNA-DSB in LCL with a BRCA1 mutation was found. However, these results do not generally exclude DNA-DSB repair deficiency in these cell lines because the methods applied have limited sensitivity and only measure the speed but not the fidelity of the repair process.